Decentralization is a business problem, not a technical problem. Engineers tend not to see this because we're engineers and so we see technical problems first.
Usenet had no economic model. All the problems you list are solvable if there were funding available to solve them.
Free volunteer developer work tends to stop at the level of polish with which developers are comfortable, which is usually command line interaction and fairly manual processes. Developers generally have to be paid to develop new features and polish those features for the general audience, which is why there are precious few open source systems used by anyone other than developers.
Those that do exist tend to be subsidized by huge companies for the purpose of "commoditizing your compliments" or as tools to herd users into an ecosystem that has upsell opportunities built into it. Examples: Chrome, any open source client for a SaaS service, etc.
Non-profits can fund to some extent, but the truth is that polished feature-rich easy to use software is extraordinarily expensive to produce. A system that a developer can create in their spare time might cost millions to render usable to non-developers. Computers are actually very hard to use. We just don't see this because we're accustomed to it. Making them easy to use is a gigantic undertaking and is often far more difficult and complex than making something work at the algorithmic level.
Centralized systems with built-in economic models like SaaS or commercial software tend to triumph because they can fund the polish necessary to reach a wider audience. A wider audience means exponentially larger network effects. See Metcalfe's Law.
Cryptocurrency could have offered an alternative model but failed for entirely different reasons: perverse incentives that attract scammers. In crypto by far the most profitable thing to do is build a fake project that can appear just credible enough to attract retail buyers onto whom you can dump your tokens. There is no structural incentive to stick with a project and really develop it because all the money is made up front through the initial offering. This also ruins the ecosystem because "the bad chases away the good." Scammers make legitimate people not want to go anywhere near crypto, transforming the whole ecosystem into a "bad neighborhood."